In the past, many efforts have been made to imitate the natural coalification of biomass, which takes place on a time scale of some hundred (peat) to hundred million (black coal) years. Besides the formation of charcoal by pyrolysis of dry biomass, the so-called hydrothermal carbonization (HTC) process for the manufacture of coal or coal-like materials has recently attracted increasing attention. The first experiments were carried out already in 1913 by Bergius, who described the hydrothermal transformation of cellulose into coal-like materials. More systematic investigations were later performed by E. Berl et al. (Ann. Chem., 493 (1932), pp. 97-123; Angew. Chemie 45 (1932), pp. 517-519) and by J. P. Schumacher et al. (Fuel, 39 (1960), pp. 223-234). Recently, the hydrothermal carbonization has seen a renaissance starting with reports on the low temperature hydrothermal synthesis of carbon spheres using sugar or glucose as precursors (Q. Wang et al., Carbon 39 (2001), pp. 2211-2214 and X. Sun and Y. Li, Angew. Chem., Int. Ed. 43 (2004), pp. 597-601). Furthermore, metal/carbon hybrid nanostructures, such as nanocables prepared by a hydrothermal carbonization co-reduction process using starch and noble metal salts such as AgNO3 as starting materials were described by S. H. Yu in Adv. Mater 16 (2004), pp. 1636-1640. H. S. Qian et al., in Chem. Mater 18 (2006), pp. 2102-2108 reported the synthesis of Te@carbon-rich composite nanocables and carbonaceous nanofibers by the hydrothermal carbonization of glucose. Moreover, M. M. Titirici et al., in New J. Chem., 31 (2007), pp. 787-789 described the catalyzed HTC as an attractive alternative for the sequestration of carbon from biomass to treat the CO2 problem.
Owing to the high local availability, the low costs and the fact that it is a carbon dioxide neutral material, hydrothermal coal or coal-like materials are a most attractive energy and carbon resource.
There are some reports in the literature, whereby biomass has been used as a source of synthetic building units for preparing e.g. resins.
For instance, U.S. Pat. No. 4,098,765, U.S. Pat. No. 4,201,699, U.S. Pat. No. 4,201,851, U.S. Pat. No. 4,200,723 and U.S. Pat. No. 4,201,700 relate to certain resins which have been obtained using extracts of certain type of biomass such as pecan nut shell extract.
FR-A-2 556 344 relates to a method of the production of a mixture of furfural and hydroxymethylfurfural, which comprises the hydrolysis of lignocellulosic material in an acidic medium in the presence of one or more ketones as solvents. The patent application further describes the hydrogenation of the furfural and hydroxymethylfurfural to give furfuryl alcohol and bishydroxymethylfuran. The mixture of furfural and hydroxymethylfurfural, the mixture of furfuryl alcohol and bishydroxymethylfuran or both mixtures so obtained can be utilized to prepare resins such as furan resins, e.g. resol-type furan resins, or, together with phenol, to prepare phenolic novolac-type resins.
According to the English abstract, CN 1737029 relates to a plant shell biomass-phenol-formaldehyde resin and its preparation. The resin is prepared by pulverizing plant shell biomass, adding an activity protecting agent (such as melamine, polyvinyl), heat treating at normal pressure, adding water, nucleophilic reagent (such as NaOH, phenol or melamine), basic or acidic catalyst, heat treating at normal pressure, and adding phenol or resorcinol and formaldehyde for polymerization to obtain the final product. It is the purpose of this patent application to retain the texture of the plant shell biomass. This is accomplished by using reaction temperatures as low as typically about 100° C. Hydrothermal coal is not, and cannot be obtained. The reaction conditions used are such that the surface of the starting biomass powder is activated but are insufficient to achieve a coalification of the bulk of the material.
The post-functionalization of carbon materials is also known.
WO 01/59008, for instance, relates to asphalt products comprising a bio-binder and a petroleum asphalt. The bio-binder is a liquefied bio-binder prepared from biomass material by direct liquefaction or fast pyrolysis of the biomass material. Prior to blending with a petroleum asphalt to give the asphalt product, the liquefied bio-binder may be blended with a coupling polymer, e.g. unsaturated fatty acids, such as safflower oil.
S. Deng and Y. P. Ting in Langmuir 21 (2005), pp. 5940-5948 describe the modification of fungal biomass by graft polymerization of acrylic acid on the surface of the ozone-pretreated biomass.
The modification of ordered hydrothermal carbons by chloroamination with 3-chloropropylamine was studied by M.-M. Titirici et al. in J. Mater. Chem. 17 (2007) pp. 3412-3418. The ordered hydrothermal carbon materials were synthesized using SBA-15 as a starting material. The pores of the as-synthesized SBA-15 template were completely or partially filled with aqueous solution of furfural. Then, the resulting furfural/SBA-15 wet sands were placed in glass vials mounted inside stainless steel autoclaves, which were heated in an oven at 180° C. for 24 h. The resulting products were filtered, washed and dried, and the silica was removed from the composites using aqueous solution of ammonium hydrogen difluoride. The obtained materials were then subjected to chloroamination.
WO 2007/104798 relates to polysaccharide-derived carbonaceous materials called “Starbons”. The Starbons are produced from polysaccharides, in particular starch, by carbonization, e.g. in the presence of a catalyst such as an acid catalyst. The as-synthesized Starbons can be post-treated with sulfuric acid so as to form sulfuric acid functions on the surface thereof. Furthermore, a cyano group containing moiety may be grafted to the Starbon and subsequently hydrolyzed to give a carboxylic acid functionalized carbon.
The above references suggest the post-functionalization of as-synthesized carbonaceous material. They are not concerned with the preparation of hydrothermal coal-like material from biomass.
U.S. Pat. No. 5,194,069 deals with the preparation of carbon powders from finely divided base material of organic origin. After pre-drying, the base material is heated to a temperature of 800 to 900° C. to decompose the same by carbonization into carbon powder and reaction fluids. Then, the carbon powder is cooled. According to a preferred embodiment, the cooling step further includes additional treatment of the obtained carbon powder such as mixing with organic and/or inorganic materials. For instance, the carbon powder may be mixed with sawdust, spices, water and, optionally, fat. By way of simple mixing, the mentioned materials cannot be incorporated in the carbon structure, as such.
As can be seen from the above, according to the literature; any modification of the conventional process of preparing hydrothermal coal-like material by incorporating a further copolymerizable compound in the structure so as to obtain hydrothermal hybrid material has not yet been attempted.
There was a strong demand to provide hydrothermal, in particular coal-like, materials, the properties and the preparation process of which can be adjusted easily.